Lightning arrester



8, 1940- F. B. JOHNSON LIGHTNING ARRESTER INVENTOR Ee derr'cl B. John son.

ATTORNEY Filed Dec. 23, 1938 .9 13 Insulation WITNESSES: WW 7. K

Patented Oct. 8, 1940 UNITED STATES LIGHTNING ARRESTER- Frederick B. Johnson, Murrysville, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 23, 1938, .Serial No. 247,422

9Ciaims.

The present invention relates to lightning arresters, and more particularly to means for improving the contact conditions between adjacent lightning arrester elements and for supporting and centering them in the casing.

A well known type of lightning arrester consists essentially of a spark gap assembly which is adapted to insulate the arrester from the line under normal conditions but to break down when a surge voltage is applied to it and permit the passage of current through the arrester, and a resistance or valve element in series with the gap assembly. The resistance element is made of material having valve characteristics, that is, one which is capable of discharging heavy currents when a high surge voltage is applied to it, but which reduces the current to a value which the gap can readily interrupt when the voltage drops to approximately the normal line voltage or the rated voltage of the arrester. The valve element is usually made up of a plurality of blocks of suitable material, such as granular silicon carbide molded with a suitable binder and baked or fired to form a porous block. A sumcient number of gaps and blocks are used in series to obtain the desired voltage rating.

Electrical contact between adjacent blocks or other elements of the arrester is obtained by means of contact plates on the elements which contact each other when the arrester is assembled. These plates are usually provided on the blocks in the form of a metallic coating applied to the end of the block, preferably by spraying, so as to obtain intimate contact with the block material. This coating is necessarily of somewhat less diameter than the diameter of the block, so that an uncoated portion remains around the periphery of the block.

It has been found that the contact conditions between adjacent blocks or between the blocks and other elements of the arrester have a very great influence on the life of the arrester. When a surge current passes through a'block, the contact cdating on the block and the adjacent contact plate are at the same potential because of their high conductivity and their intimate contact. The uncoated peripheral portion of the block, however, may be at a different potential because the passage of current through the relatively high resistance material of the block causes a potential gradient to exist in a radial direction between the edge of the coating and the edge of the block. If this uncoated portion is accidentally in contact with the adjacent arrester element or it it is close enough to it, sparking may occur because of the difference in potential due to this potential gradient. This sparking may, and often does, induce flashover of the block, especially in surges of relatively long duration, which may cause failure of the block and in many cases of the entire arrester.

It is an'object of the present invention, therefore, to provide means between adjacent blocks or other lightning arrester elements which will prevent contact or sparking between those parts of the adjacent elements which may be at dif-, ferent potentials but which will provide good electrical connection between the elements. In this way the life of the blocks and of the arrester is greatly increased by removing the danger of flashover from this source.

A further object of the invention is to provide a spacing member between adjacent blocks or other arrester elements which will also serve to support the blocks in the casing and to maintain them spaced from the casing and centered therein. It is desirable in assembling lightning arrester elements in a porcelain casing to hold the parts spaced from the wall of the casing in order to prevent abrasion and breakage, especially in long units. This has been done by pouring melted wax into the casing in the space between the blocks and the casing and allowing it to harden. This construction, however, introduces a hazard in case of flashover of one or more of the blocks, since the dissipation of the surge energy in the wax causes it to volatilize and produce high internal pressures in the casing. In some cases this pressure may become high enough to rupture the porcelain casing with explosive force, thus oreating a serious hazard to surrounding structures. The use of wax also has the disadvantage that it cannot be used tospace the gap structure from the casing, if this is desired, because of the danger of penetration of the hot wax into the gap units.

A spacing member is, therefore, provided by the present invention which may be placed between adjacent blocks or between other arrester elements, such as gap units, to space them from the casing and center them therein, and which also serves to improve the contact conditions between the arrester elements by preventing accidental contact or sparking between those parts of adjacent elements which may be at difi'erent potentials, while at the same time it provides good electrical connection betweenthe adjacent description, taken in connection with the accompanying drawing, in which:

Figure 1 is a longitudinal sectional view of a lightning arrester unit,

Figs. 2 and 3 are a top viev and an edge view, respectively, of the spacing element of the present invention, and

Fig. 4 is an enlarged, sectional view showing the assembly of the spacing element between two adjacent arrester blocks.

Figure 1 shows a typical lightning arrester assembly in which the spacer oi the present invention may be used. The lightning arrester shown in this figure may be a complete unit in itself but is shown as being one unit of a high voltage station type lightning arrester of the type described in a patent of L. R. Ludwig et al., No. 2,135,085, issued November 1, 1938, and assigned to Westinghouse Electric 81 Manufacturing Company. This unit consists of a generally cylindrical porcelain casing I which is closed at the top by a cap member 2 and at the bottom by a base member 3, both of which are preferably of a suitable metal such as aluminum, and which are secured to the porcelain casing I by cementing or in any other desired manner.

The arrester consists of a gap assembly 4, 01 any suitable type, which is shown as being sealed in a tubular casing, as described in the abovementioned patent, and a valve element consisting of a plurality of blocks 5. These blocks may be of any suitable type having the desired valve characteristics, but are preferably made of granular silicon carbide molded with a suitable binder and baked or fired to form porous blocks. A sufllcient number of these blocks is used in series to obtain the desired voltage rating and they are assembled in the casing with the uppermost block in contact with a spring plate 6 which bears against a metal plate I at the top of the arrester in contact with the cap member 2. The gap assembly 4 rests on a similar spring plate 8 at the bottom of the unit which is supported on a plate 9 in contact with the base member 3. The valve element and gap assembly are separated by a metal spacing tube I0 and a spring plate II, the spacer in being made of the proper length so that the complete assembly including the desired number of blocks and a gap element 01' the desired length will fit tightly in the casing. The spring plates serve to maintain the various elements in intimate contact and to hold them in position in the casing.

The spacing member of the present invention is shown more particularly in Figs. 2 and 3 and consists of two discs ll of copper, or other suitable conducting material, with a larger disc or washer l3 of insulating material clamped between them. The three discs are clamped together concentrically by a rivet H of copper, or other conducting material, which passes through them and is flattened down flush with the discs I2 on each side. The disc or washer i 3 is made of a stiff, but non-rigid, insulating material, such as the material known as Vellumoid, and is of greater diameter than the inside of the casing I. A plurality of radial notches I5 is provided around the periphery of the disc l3 and the diameter of the circle defined by the inner ends of these notches is made approximately equal to the diameter of the blocks 5. The diameter of the discs I! is made somewhat less than that of the contact coatings on the blocks 5 so that they will contact these coatings only.

In assembling the arrester, a spacer element is placed between each block and the adjacent block or other element, and also between any other adjacent arrester elements which it is desired to space from each other and from the casing in this manner. Since the diameter of the disc II is greater than that of the casing I, the disc cup shaped member, as clearly shown in Fig. 4, the radial notches permitting this bending. The notches define the shape of the bottom of the cup so that the block contained in it is positioned in the center of the cup and thus spaced from the casing and centered therein, while the contact coating H of the block is positioned c0ncentrically with the disc II. The discs I! are in contact with the contact coatings or plates ii of the adjacent elements and the rivet l4 joining these discs provides a good electrical connection between them while the insulating disc l3 extends between the uncoated peripheral portions of the blocks, and thus separates those portions of adjacent blocks or other elements which may be at diiferent potentials and effectively prevents any sparking which might otherwise occur between them. Since the diameter of the discs I2 is made less than that of the adjacent contact plate or coating l6, they will contact this coating only and there will be no possibility of contact or sparking between elements or portions of elements which are at different potentials, so that the danger of flashover of the blocks induced in this manner is entirely eliminated.

It will be seen, therefore, that a spacing member has been provided for lightning arrester blocks or other arrester elements which acts as a simple and eifective means for spacing them from the casing and centering them therein, while at the same time it serves to improve the contact conditions by preventing contact or sparking between portions of adjacent elements which may be at diflerent potentials and which thus greatly increases the life of the unit. This spacer element also acts as an isolator which may prevent a block failure from spreading to adjacent blocks.

It is to be understood that although a specific embodiment of the invention has been illustrated and described, it is not limited to the exact structure or arrangement shown but is capable of various modifications. ber may be used as a centering device for two ad- J'acent blocks by bending the tabs formed by the peripheral notches alternately up and down. The invention is, therefore, not limited to the exact embodiment shown broadest aspects it includes all equivalent modifications and embodiments which come within the scope of the appended claims.

I claim as my invention:

1. A lightning arrester comprising a casing, a plurality of lightning arrester elements disposed in the casing in series relation, and spacing members between adjacent elements for spacing them from the case and centering them therein, each of said mmbers having plates of conducting material in contact with the adjacent elements and a disc of still insulating material held between the plates and adapted to contact the inside of the casing.

2. A lightning arrester comprising a casing, a plurality of lightning arrester elements disposed in the casing in series relation, and spacing members between adjacent elements for spacing them from the case and centering them therein, each of said members having two plates of conducting Thus one spacing memand described but in its material in contact with the adjacent elements, the plates being of less diameter than the contact surfaces of the elements, and a disc of stifl insulating material held between the plates, said disc being of greater diameter than the inside of the casing, whereby it will contact the case and maintain the elements centered therein.

3. A centering member for use in a lightning arrester having a plurality of elements arranged in series relation in a casing, said member comprising two metal discs of less diameter than said elements and a disc of stifl insulating material of greater diameter than the inside of the casing, said disc of insulating material being clamped concentrically between the metal discs.

4. A centering member for use in a lightning arrester having a plurality of elements arranged in series relation in a casing, said member comprising two metal discs of less diameter than said elements, a disc of stiff insulating material of greater diameter than the inside of the casing and having radial notches about its periphery, said disc of insulating material being positioned between the metal discs and concentrically therewith, and a metal clamping member extending through all of said discs.

5. In a lightning arrester, a casing, a plurality of blocks of resistance material disposed in series relation in the casing, each of said blocks having a conducting coating on each end thereof, the area of the coating being less than that of the blocks whereby the peripheral portions of the blocks are uncoated, and spacing members between adjacent blocks, said members having conducting portions of smaller diameter than the conducting coatings of the blocks and having insulating portions which separate the uncoated portion of each block from the adjacent block.

6. In a lightning arrester, a casing, a plurality of lightning arrester elements disposed in series relation in the casing, and an insulating washer placed between certain of said arrester elements, said washer being of greater diameter than the casing whereby it may be forced into intimate engagement with the walls of the casing and having conducting members secured on each side thereof to make contact with the adjacent arrester elements, said conducting members being electrically connected together.

7. In a lightning arrester, a casing, a plurality of lightning arrester elements disposed in series relation in the casing, and an insulating washer placed between certain of said arrester elements, said washer being of greater diameter than the casing whereby it may be forced into intimate engagement with the walls of the casing and having conducting members secured on each side thereof to make contact with the adjacent arrester elements. said conducting members being secured to the insulating washer and to each other by a clamping device which also provides electrical connection between them.

8. A spacing member for use in a lightning arrester having a plurality of elements disposed in series relation in a casing, said member comprising-a washer of insulating material of greater diameter than the casing and conducting members secured on each side of the washer and electrically connected together.

9. A spacing member for use in a lightning arrester having a plurality of elements disposed in series relation in a casing, said member comprising a washer of insulating material of greater diameter than the casing and conducting members on each side of the washer, said conducting members and washer being joined together by a fastening means which also provides electrical connection between the conducting members.

FREDERICK B. JOHNSON. 

